Return bend



May 23, 1961 c, sc u 2,985,017

RETURN BEND Filed March 2, 1959 INVENTOR HEP/mu 6. 50/1/77 32 r Mm ATTRNEY United States Patent Ofitice 2,985,017 Patented May 23, 1961 RETURNBEND Hermann C. Schutt, 399 Belknap Road, Franiingham, Mass.

F lied Mar. 2, 1959, Ser. No. 796,405

2 Claims. (Cl. 73-343) My invention relates to return bends and moreparticularly to an improved return bend adapted to accommodate a housingprojecting into the bend for the reception of a heat-sensitive element.

In the construction of apparatus for carrying out various chemicalprocesses employing heat it is necessary, in order to control theprocess to measure the temperature accurately. This is commonly done byintroducing a housing or tubing into the conduit through which the fluidbeing processed or the reactants flow. This housing is commonly known asa thermowell. Any appropriate temperature-sensing means may bepositioned in the thermowell. Advantageously a thermocouple junction maybe positioned in the thermowell adapted to produce a voltage which is afunction of the temperature .to which the junction is heated. Suchthermocouples may then be used automatically to control processconditions.

Most modern furnaces and heat exchangers are made of straight tubingjoined at their ends by return bends, which may customarily change thedirection of flow either through 180 or 90, although it is to beunderstood that any change in direction of flow may be chosen dependingon the design of the particular equipment. It will be clear to thoseskilled in the art that thermowells may advantageously be positioned inthe return bends since these are positioned at the extremities of thetubes and are thus readily accessible for insertion, removal orreplacement of said thermowell and attachment of lead wires or conduitsfor the electrical or mechanical impulses created by the temperature.

It has been found that fluids flowing at high velocities and heated tohigh temperatures will erode thermowells. In addition to the erosion ofthe fluid itself, such fluids frequently carry abrasive particles suchas finely-divided catalyst particles, or particles of carbon or othersolids formed in the course of a conversion process. This erosive eifectis particularly severe in the pyrolysis of hydrocarbons wheretemperatures as high as l,600 F. and flowing velocities in the order of1,009 feet per second may be encountered. In .addition to the hightemperatures of the process, super-atmospheric pressures are employedand if the thermowellfails due'to erosive wear, reactant will escapeinto the atmosphere.

investigations of disastrous fires at oil refineries have shown'that inmany cases they are directly attributable to the failure of thermowells.The escape of superheated hydrocarbon vapors .into the atmosphere willspontaneously produce .a violent .flash fire which willignite .any

combustibles in the environment.

Many efforts have been made to solve the problem of preventing theerosion of thermowells in return bends. It has been suggested toposition a thermowell in the return bend inward of the outer wall of thereturn bend and perpendicular to the reactant flow. In this manner heavyparticles would be thrown clear of the thermowell by centrifugal forceto the outer wall. Unfortunately, erosion will occur even in absence ofheavy particles since lighter or finer particles which will not beappreciably affected by the centrifugal :force are nevertheless quiteabrasive. The abrasive elfect moreover is enhanced by elevatedtemperatures where metals become softer.

One object of my invention is to provide an improved return bend adaptedto protect an inserted thermowell from erosion.

Another object of my invention is to provide an improved return bendformed with an integral baflie for protecting a thermowell inserted intothe return bend adjacent to the bafile.

Other and further objects of my invention will appear from the followingdescription:

In general my invention contemplates the provision of a battle in theinterior of a return bend positioned on the upstream side of the bend.The bafile may advantageously be formed in the shape of a rib integralwith the return bend and preferably formed by casting. The rib baflle isadapted to divert the fluid stream from the thermowell and thus shieldit from the impact of the fluid passing through the return bend and theimpingement of solid particles Whose impact is augmented by centrifugalforce. The return bend casting is normally provided with a boss to whichan external housing may be Welded, or

otherwise secured. The baflling rib may be shaped to follow thecurvature of the bore through the boss and return bend wall.

In the accompanying drawings which form part of the instantspecification and which are to be read in conjunction therewith and inwhich like reference numerals are used to indicate like parts in thevarious views:

Figure l is a sectional elevation of my improved return bend in use,showing one embodiment of my invention.

Figure 2 is a fragmentary sectional View taken along the line 22 ofFigure 1.

Figure 3 is a sectional View taken along the line 3-3 of Figure l withthe thermowell and the thermowell housing removed.

Figure 4 is a fragmentary sectional view drawn on an enlarged scaletaken along the line 44 of Figure 2 with the thermowell in place.

Referring now to Figure 1, the return bend, indicated generally by thereference numeral It may be formed of any appropriate material.Advantageously in the present invention the return bend should be madeof cast steel, austenitic manganese steel, chrome-molybdenum steel,chrome-nickel steel or special hard alloys such as Stellite, which is analloy containing cobalt, chrome, tungsten and molybdenum.

I prefer to use cast steels, and cast alloy steels, since castings havehigher hardness and resistance to erosion at any given temperature thanwrought materials of the same chemical composition. The hardness of castmaterials at elevated temperature is usually 2 to 2.5 times greater thanthat of the wrought alloy of which the thermowells are usually made.

The return bend comprises a body member 12 formed with a curvedpassageway .14. The passageway may curve through any appropriate angle.Normally return bends are formed to curve through angles of either 180or Figure 1 shows a turn return bend. The passageway 14 is provided withan outlet opening 16 and an inlet opening 18. In use, a tube 20, formedof any appropriate material such as wrought alloy steel, is welded tothe outlet opening 16 by means of a weld 22. Similarly a tube 24 iswelded by means of weld 26 to the inlet opening 18. The arrows in Figure1 show the direction of flow of the fluid from tube 24 through thepassageway 14.

The body member 12 is also formed with a bore 30, the axis of whichextends in the direction of the inlet of the passageway 14 adjacent tothe inlet opening 18.

Advantageously the bore 30 is positioned coaxially with the axis of thepassageway 14 at the inlet opening 18; that is, coaxially with tube 24.It is understood, of course, that the bore 30 'may communicate with thepassageway 14 at any desired point in the passageway 14 as long as thebore 30 extends in the direction of or substantially in the direction ofthe passageway at its inlet opening 18.

The purpose of bore 30 is to provide means for inserting the thermowell,in which the thermocouple or other temperature-sensitive measuring meansis positioned, into the passageway 14. As shown in Figure 1 the bore 30is formed with a boss 32 to which. a tube 34 is welded by means ofcircular weld 36. It is understood, of course, that the tube 34 may besecured to the boss 32 in any other appropriate manner such as by screwthreads or the like. The tube 34 forms a housing for the thermowell. Acircular plate 38 is welded to the tube 34 forming a flange. Thethermowell 40 itself is formed of a smaller diameter than the bore ofhousing 34 and bore 30 which is coextensive therewith, as can readily beseen by reference to Figure 1. It may be formed in the shape of anelongated chamber of any appropriate hard material, as shown in Figure1.

The outer end of the thermowell 40 is provided with a flange 42 securedthereto in any appropriate manner, such as welding or the like. Acircular sealing ring 34 is clamped between the flanges 42 and 38 bymeans of bolts 46. The upstream side of the thermowell 40 would normallybe subjected to erosion and abrasion in use. I cast a rib '0 integralwith the body member 12 adjacent to the inlet opening 18. This rib isslightly wider than the exterior diameter of the thermowell 40. Inpractice I make the rib between 0.03 inch and 0.1 inch wider than thediameter of the thermowell. The n'b will protect the wall of thethermowell projecting into the return bend from erosion by the flowingfluid. The rib also acts as a baffle diverting the fluid and solidparticles carried thereby. Advantageously I curve the upper surface 52of the rib 50 so that it conforms with the curvature of the surface 54of thebore 30. Owing to the fact that the internal diameter of the bore30 is larger, a space 60 will be provided through which vapors orreactant may pass into the thermowell housing 34. The space 60 makes forease of insertion and removal of the thermowell.

In order to prevent coke and solid particles from accumulating betweenthe thermowell and the batflling rib 50 and return bend body 12, Iprovide an arcuately molded filler 70. This filler may be made of anyappropriate heat-resistant material. Advantageously it may be made ofasbestos fiber impregnated with a silicone resin in partiallypolymerized form, which is adapted to set by heat to form a heat stablelayer of resin bonded asbestos fiber. Any appropriate filler materialmay be employed, as will be readily understood by those skilled in theart.

It will be observed that the outer end 41 of the thermowell 40 is formedof increased Wall thickness since it will be subject to directimpingement by fluids flowing through the inlet tube 24.

The rib may be made with a streamlined nose, as can readily be seen byreference to Figure 3, so as to reduce resistance to flow of the fluidpassing through the return bend at the same time parting the fluid in astreamline pattern reducing any erosive action on the rib itself.

It will be seen that I have accomplished the objects of my invention. Ihave provided an improved return bend in which a thermowell can beconveniently inserted and which will protect. the thermowell fromabrasion and erosion from fluid passing through the return bend. Mythermowell may be rapidly and expeditiously removed and replaced forinspection and will have much longer life when used in my improvedreturn bend.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of myclaims. It is further obvious that various changes may be made indetails within the scope of my claims without departing from the spiritof my invention. It is therefore to be understood that my invention isnot to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

1. A return bend for receiving a thermowell having an exterior diameterincluding in combination a steel casting formed with a curved internalpassageway having an inlet opening and an outlet opening, a bore formedin said casting communicating with said passageway, said bore having adiameter larger than said exterior diameter, a rib integral with saidcasting positioned in said passageway extending from a wall of thepassageway adjacent said inlet opening toward said bore, said rib beingformed with a concave upper surface substantially forming a continuationof a portion of the interior surface of said bore, said rib having athickness substantially equal to said exterior diameter of thethermowell, said bore being adapted to receive said thermowell with saidthermowell disposed over said rib concave surface, and filler materialon the surface of said rib.

2. A return bend for receiving a thermowell having an exterior diameterincluding in combination a member formed with a curved internalpassageway having an inlet opening and an outlet opening, a bore formedin said member communicating with said passageway, said bore having adiameter larger than said exterior diameter, a rib carried by saidmember positioned in said passageway extending from a wall of thepassageway adjacent said inlet opening towards said bore, said rib beingformed with a concave upper surface substantially forming a continuationof a portion of the internal surface of said bore, said rib having athickness substantially equal to said exterior diameter of saidthermowell, said bore being adapted to receive said thermowell with saidthermowell disposed over said rib concave surface.

References Cited in the file of this patent UNITED STATES PATENTS301,964 Colby July 15, 1884 318,971 Evans June 2, 1885 490,723 RoneyJan. 31, 1893 779,398 Calkins Jan. 3, 1905 941,596 White Nov. 30, 19091,079,724 Roberts Nov. 25, 1913 1,193,911 Machlet Aug. 8, 1916 1,226,427White May 15, 1917 1,441,581 Hilligardt Jan. 9, 1923 1,615,480 PooleJan. 25, 1927 2,015,968 Ryder Oct. 1, 1935 2,560,455 Knight July 10,1951 2,732,331 Wesh Jan. 24, 1956

